These types of surface measuring devices are generally known, and are used for measuring, for example, the contour or roughness of the surface of workpieces.
The measurement of the surface of a workpiece often takes place using moving measuring probes. Tactile mechanical probes or probes that operate without contact, for example distance sensors that operate optically or pneumatically, may be used.
The relatively large measuring circuit is subject to external and internal disturbances which manifest as measurement noise or basic interference. The disturbances occur as oscillations whose component parallel to the probe deflection and perpendicular to the feed direction is superimposed on the sampled workpiece profile as a measurement deviation.
The oscillations are on the one hand externally excited by vibrations that are transmitted via the foundation or through the air to components of the surface measuring device, primarily to the base plate thereof. To prevent further transmission of these oscillations, the base plate is frequently supported with isolation from oscillations, although the extent of the insulation when the surface measuring device is set up in the vicinity of production machines is often not sufficient.
On the other hand, the oscillations are excited by the motor itself or components of a gear system of a feed apparatus of the surface measuring device.
The intensity of the excitation generally increases with increasing feed rate. This component of the oscillations typically dominates the overall disturbances when the measuring station or the surface measuring device is present under laboratory conditions. In contrast, when the surface measuring device is set up near production facilities, the external disturbance component predominates.
The extent to which the probe in the measuring circuit responds to these oscillations is determined primarily by the presence of mechanical resonances or natural oscillations. It is unfavorable when frequency components from the oscillation excitation coincide with resonance lines of the measurement assembly in the frequency band to be transmitted.
Measuring tasks in parts of the automotive industry often require measuring circuits or dimensions in the range of several decimeters. In conjunction with properties such as the modulus of elasticity, damping, and specific weight of the materials used, natural resonances of the measurement assembly at the location of the probe result even at several tens of Hz. However, these frequencies lie completely in the typically used bandwidth of the electrical measuring system. Its limiting frequency is often in the range of approximately 100 Hz, and occurs at even higher frequencies when optical probes are used.
The oscillations that occur thus result in measurement deviations that are superimposed on the useful signal, which corresponds to the profile of the sampled surface. After the measurement, surface characteristic values are computed from a surface profile that is measured by means of the surface measuring device. In particular when the surface measuring device is set up near production facilities, the surface characteristic values determined in this way may be so greatly skewed that an operationally reliable assessment of the surface properties is no longer possible.
In terms of high measuring accuracy, it is therefore desirable to reduce the influence of oscillations on the measuring result to the greatest extent possible.
In terms of reducing the oscillations, a measuring station should have a preferably high natural resonance. In this regard, it is known from DE 10 2010 023 354 A1 to provide measures that result in a more rigid and lightweight design of a probe arm, and that, among other things, have a positive effect even in the range of higher natural oscillations.
Oscillation insulation systems are used against oscillations that are caused by external sources. Such oscillation insulation systems are generally situated between the foundation of the installation site of the surface measuring device and the base plate of the measuring system of the surface measuring device. These types of oscillation insulation systems are often implemented as a combination of soft suspension with respect to a heavy mass. Above the natural resonance of the insulation system, the oscillations introduced into the foundation are further transmitted into the base plate of the measuring system, but in attenuated form.
However, such an oscillation insulation system always provides only one finite damping factor for each excitation frequency. Thus, in the strict sense of the term, the oscillations are not kept away from insulation, and instead are merely further transmitted in attenuated form. As a result, an oscillation insulation system that performs its task under laboratory or measuring room conditions is often no longer sufficient overall for a setup near production facilities.
A further disadvantage of such oscillation insulation systems is that they require a high outlay of construction effort and equipment at the installation site of the measuring station or the surface measuring device. Thus, for mobile surface measuring devices that may be set up at different locations, it is not meaningful to use such oscillation insulation systems.